So I have a 1983 Mercedes 300sd I recently had a hard start and rough idle and white smoke: was told to replace the glow plugs and did so with NGK glow plugs car ran better but still hard start unless I used the eng block heater and now it won’t start at all. Purged the fuel system for air and still no start. Checked power to glow plugs 2 only have power so I checked the relay and it is only sending power to those 2. Could this cause it not to start even though it’s 98 degrees out here ?

It should start at 98 degrees, without glow plugs. However, it will likely be more cranking. Is this issue something that just started or has it been an ongoing problem?

If it's just started, I would suspect a fuel problem. Do you have any fuel leaks, especially around the primer pump? The older white style is notorious for leaking fuel and getting air into the fuel system.

How does the in-line fuel filter look? Any black debris? Any history of waste veggie oil use?

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

It stared about 3 weeks ago with a hard long rank to start and then rough idle. Changed glow plugs 3 days ago smoother idle but still prolonged start. 2 days ago wife ran out of fuel put fuel in got it started went to gas station and filled it up got to our destination in FL and next morning would not start plugged in heater over night and this morning still no start.

red about 3 weeks ago with a hard long rank to start and then rough idle. Changed glow plugs 3 days ago smoother idle but still prolonged start. 2 days ago wife ran out of fuel put fuel in got it started went to gas station and filled it up got to our destination in FL and next morning would not start plugged in heater over night and this morning still no start.
I bypassed the in-line filter do to leak getting new one tomorrow

Since the car was run out of fuel, the tank strainer screen may have become clogged. The easiest way to rule it out is to connect a portable Fuel can near the engine, prime, and see if it will start and run smoothly.

First of all get the glow plugs working properly. Some diesel engines do not even like to start even hot without at least a little glow plug input. I had one once. Never found the reason or really bothered looking for it. Engine seemed to have decent compression and worked well otherwise.


That function has to be repaired anyways plus could be your problem. Other than bosh replacement glow plugs have had issues as well. NGK may be okay but I do not know. They have a decent reputation for spark plugs but I do not know if any other members have tried NGK glow plugs.